1. Technical Field
The disclosure relates to a multi-layered film, a backsheet for photovoltaic modules, a method of manufacturing the same, and a photovoltaic module comprising the multi-layered film.
2. Related Art
Recently, much attention has been paid to renewable and clean energy because of global environmental problems and exhaustion of fossil fuels. Among these, solar energy has attracted attention as a representative pollution-free energy source which can solve the problems of environmental contamination and exhaustion of fossil fuels.
A photovoltaic cell to which a principle of photovoltaic power generation is applied is a device configured to convert sunlight into electric energy. Since the photovoltaic cell is exposed to external environments for a long time to facilitate absorption of sunlight, it is manufactured into a unit by performing several packaging processes to protect the cells. The unit is referred to as a photovoltaic module.
Generally, a backsheet having excellent weather resistance and durability is used for the photovoltaic modules to stably protect the photovoltaic cell during long-term exposure to external environments. Such a backsheet generally includes a backsheet in which a resin layer including a fluorine-based polymer such as polyvinyl fluoride (PVF) is stacked on a substrate.
However, the PVF resin has poor adhesion to a polyethylene terephthalate (PET) film typically used as a substrate for the backsheet. Thus, a fluorine-based polymer film obtained by extrusion or casting is laminated on a substrate using a urethane-based adhesive, and used as the substrate. However, this requires the use of expensive film preparing equipment, an adhesive and the application of additional adhesive coating and laminating processes. In addition, a film having a higher thickness than that is required to facilitate handling of the film should be used during the preparation of a film, the use of various additives and fillers are limited, and a high processing temperature is required.
On the other hand, even when a fluorine-based polymer film, which is prepared in the form of a resin suspension or solution, is coated and dried on a substrate, a solvent having a high boiling point is generally used, and thus a high drying temperature of 200° C. or higher is required.
A large amount of energy is used to apply high-temperature heat to a PVF resin solution, which requires a high drying temperature. Accordingly, this increases the production costs of the backsheet for photovoltaic modules and also inflicts thermal shocks on a substrate or causes thermal deformation of the substrate, thereby degrading the quality (e.g., mechanical characteristics, etc.) of the product and rapidly deteriorating the mechanical properties over a long-term outdoor use.
Therefore, there is continuous demand for a material of the backsheet for photovoltaic cells, which has excellent durability and weather resistance and can be dried at a low drying temperature, so that the production costs can be reduced and the productivity and quality of the photovoltaic module can be improved.